Mounting for piezo-electric devices



NW 19% R. s. OHL 1,783,131

MOUNTING FOR PIEZO ELECTRIC DEVICES Filed Sept. 23, 1926 1: I L I: I P B7 6 fig. G #82 INVENTOR. 13?. 6. 0% BY A TTORNEY Patented Nov. 25, 1930 UNITED STATES PATENT OFFICE RUSSELL S. OHL, OF NEW YORK, N. Y., ASSZGNOR '50 AMERICAN TELEPHONE AND TELE- GRAPH COMPANY. A CGZZPOR-ATION 6F NEV] YORK MOUNTING FDR PIEZQ-ELECTBIC DEVICES Application filed September 23, 1326. Serial No. 137,376.

This invention relates to mountings for piezoelectric crystals or devices, and particularly to arrangements in such mountings for avoiding or greatly reducing the undesirable effects on the freei'vibratory period of the piezo-electric member caused 'by variations in the surrounding thermal conditions.

A piezo-electric device comprises a crystal of piezoelectric character which may be set 10 into vibration between two conductive electrodes. When such a piezo-electric crystal is placed between the two conductive electrodes in such a way that a gap exists between one or two of the surfaces of the piezo-electric crystal and the adjacent conductive elec- 2 the piezoelectric crystal and theadjacent conductive electrodes. In experimenting with such a crystal it has been found that as the size of the gap changed, the frequency of vibration of the piezo-electric crystal also changed withinreasonable limits.

Heretofore, .such a piezoelectric crystal was mounted between two metallic plates or electrodes in some suitable form of mounting in such a way that the gap above-mentioned was provided to permit the free vibration of the piezoelectric crystal. The size of. the gap was found to be dependent upon the rigidity of certain insulating material, such as hard rubber, bakelite, etc., used for the base of the mountin Moreover in the mountin s heretofore used for piezo-elec'tric devices, the external thermal variations brought about expansions and contractions of the elements of the mounting, causing uncontrollable changes in the size of the gap existing between the piezo-electric crystal and its adjacent conductive plates or electrodes Due to such changes in the external thermal conditions, the piezoelectric crystal continually assumed a difi'erent vibratory period.

One of the principal objects of this invention is the provision of means in such forms of mountings for piezo-electric devices where'- in the undesirable effects of temperature variation on the free vibratory period of a piezoelectric crystal contained therein are avoided or substantially reduced.

Another of the objects of this invention is the provision of means for adjusting the size of the gap existing between the conductive electrodes and the piezoelectric crystal therebetween so that the vibratory period of the piezoelectric device may be changed .as conditions necessitate, said adjustments being independent of external temperature variations.

In my copending application, Serial No. 137,377, iled September 23, 1926, I have shown, described and claimed a piezo-electric crystal mounting having a pair of electrodes spaced by a definite distance and the spacing of theseelectrodes is maintained substantially constant and invariable even during exteral temperature variations.

i fhile this invention will be pointed out with particularity in the appended claims, the invention itself, both as to its further objects and features, will be better understood from tie detailed description hereinafter following, when read in connection with the accompanying drawing, showing a cross-sectional view of a moun ing for a piezo-electric device and the enclosed piezoelectric device, which drawing is shown herein merely for the purpose of illustration.

Referring to the drawing, there are shown two conductive electrodes P and P these electrodes forming the means for the transmission or reception of electric current to or from a piezoelectric device PE, mounted between these electrodes. It will be understood that these electrodes P and P may be of any material whatsoever, but that they are preferably of some conductive material such as brass, steel, nickel, etc. The device of piezo-electric character, PE, is so placed between the conductive electrodes P and P that a gap exists between one or both of the surfaces of the piezo-electric device PE and the adjacent conductive electrodes P and P This gap permits the free vibration of the piezo-electric device at a characteristic frequency. Yet by changing the size of this gap the vibratory period of the piezo-electric device PE may be changed as conditions necessitate, as will be shown more fully in the description hereinafter following.

The conductive electrode P is suitably fastened to a base B by meansof two screws T and T This base B may be of any material whatsoevenbut itispreferably of some insulating material, such as hard rubber, bakelite, porcelain, glass, etc. A tube or cylinder G surrounds the piezo-electric device PE and is preferably coaxial therewith, This tube or cylinder G separates the conductive electrodes P from a metallic plate L. by a preknobK-is revolved in the other direction the conductive electrode moves downwardly. Accordingly, the size of the gap between the conductive electrodesfP and P and the piezo-electric member PE placed therebetween may beadjusted as conditions necessitate. Permanently fastened to the metallic plate L is another base M, the fastening compris ing, for the purpose of illustration, two screws'l and T An indicator S is mounted on the base M and is so placed with respect to the dial D that as the dial moves injone direction or in the otherthe size of the gap may be varied and a suitable indication provided by means of the indicator S which cooperates with the dial D to readily determine the size of the gap.

V The thickness and generallateral proportionsof the'tube or cylinder G are of such magnitude that the capacity between the electrodes P and P due to the presence'of this tube or cylinder, is substantially negligible when compared with the capacity between the electrodes P and P through the piezoelectric device" PE and the gap between this device and the electrodes P and P The lengthand general longitudinal dimensions of thetube or cylinder G are so proportioned v'v threspect to the longitudinal proportions of the conductiveelectrodes P and P and i liel'inear coefficients of thermal expansion the t'ubeior cylinder G and of the conductivei electrodes P and P a re so chosen, that change in the longitudinal dimensions of the conductive electrodes P andP due to any variation in the external thermal con- ,ditions, will be equal andopposite to the change taking place-in the-longitudinal diw mensions-of the tube or cylinder G due to the same external temperature variationjAfter the -size of the-gap between the "conductive general physical .proportions of the tube or' cylinder Grand of the conductive electrodes 7 P and P are so chosen that the products of any changes in their longitudinal dimensions and their corresponding linear coefficients of thermal expansionwill be substantially equal. ,Yet it will be noted that these products may be varied so as to bear some fixed relationship to each other to bringabout any change in the size of the gap between the piezo-electric device PE and the adjacent conductive" electrodes, when a changetakes place in the external thermal conditions, all of which 'is within the scope of this invention.

It will thereforebe clear that this invention is designed to provide a mounting'for a piezo-electric device in which the frequency characteristic of the piezo-electric device may be varied as conditionsnecessitate, substantially free from variations in 'the' external thermal conditions. Such a mounting is particularly desirable where the frequency characteristic of the piezo-electric device must be brought into synchronism with the frequency characteristic in some other electrical circuit;

While this invention has. been. shown and described in one embodiment merely for the purpose of illustration, it will be understood that the general principles of this invention may be embodiedin other and widely varied organizations without i departing from the spirit of the 'inventionand-the-scope of the appended claims.

What isclai'medis:

1. A mounting for a piezo-electric device, having means associated therewith for varying the vibratory periodof said piezo-electric device as desired, said means being substantially'unafiiected by external temperature variations. M

2. A mounting for a piezoelectric device, comprising two conductive electrodes betweenwhich'aipiezo-electric device-may be 5 placed so that it may freelyvibrate therebetween, means for adj usting the distance 1 between said conductive electrodes','and means for maintaining the distance between said electrodes substantially independent of external temperature variations.

'3. "Piezoelectric apparatus including a piezo-electric device, twoelectrodes between which the piezo-electric device may be placed, agap being; provided between the} piezo eleci too tric device and one of the conductive electrodes so that said piezo-electric device may freely vibrate between said electrodes, means for varying the size of said gap in order to correspondingly vary the vibratory period of said piezo-electric device, and means for rendering the size of said gap substantially independent of external temperature variations. 7

4. Piezoelectric apparatus including a piezo-electric device, two conductive electrodes between which the piezo-electric device may be placed, a gap being provided between the piezoelectric device and one of the conductive electrodes so that said piezo-electric device may freely vibrate between said electrodes, means for varying the size of the gap existing between the piezo-electric device and the conductive electrodes, means for rendering the size of the gap substantially independent of external temperature variations, and means for determining and indicating the size of said ap.

5. Piezo-electric apparatus including a piezc-electric device, two metallic electrodes having faces disposed so that the piezo-electric device may freely vibrate therebetween and so that there may be a longitudinal move ment of these faces due to external temperature variations, a tube surrounding the piezoelectric device and coaxial therewith, said tube being made of an insulating material having a predetermined linear coefficient of thermal expansion and producing a longitudinal movement due to said external temperature variations equal and opposite to that of the faces of said metallic electrodes, and means for changing the efi'ective distance between the faces of said metallic electrodes substantially independently of external temperature variations.

6. Piezo-electric apparatus including a piezo-electric device, two metallic electrodes having faces disposed so that the piezo-electric device may freely vibrate therebetween, a cylinder coaxial with the piezo-electric device and separating the faces of the metallic electrodes by a predetermined distance, said cylinder being formed of a material having a predetermined linear coefficient of thermal expansion, any external temperature variation producing a linear movement of the faces of the metallic electrodes substantially equal and opposite to the linear movement of the cylinder separating the faces. of the metallic electrodes, and means for changing the effective distance between the faces of said metallic electrodes independently of said external temperature variations.

7. A mounting for a piezo-electric device, comprising a pair of metallic electrodes, at piezo-electric device included between said metallic electrodes so that a gap exists between the piezoelectric device and surfaces of the metallic electrodes, the piezo-electric device assuming a characteristic frequency and f'eely vibrating at that characteristic frequency, a tube having a predetermined linear coefficient of thermal expansion surrounding the metallic electrodes and the piezoelectric device, said tube effecting a linear movement of the metallic electrodes equal and opposite to the linear movement of said electrodes during any change in the external temperature conditions, and means for changing the size of the gap between the metallic electrodes and the piezo-electric device independently of said external temperature variations.

8. The combination of a pair of metallic electrodes, a piezo-electric device located between the electrodes, a gap being provided between the metallic electrodes and the piezoelectric device, a hollow cylindrical body 00- axial with said metallic electrodes and having a coeilicient of expansion such as to counteract the linear displacement of said metallic electrodes caused by external temperature variations, and means for varying the size of said gap substantially unaffected by said ex ternal temperature variations.

9. A mounting for piezo-electric bodies, comprising two conductive electrodes, means for varying the distance between said electrodes, and means for maintaining the distance between said electrodes independent of variations in the condition of the surrounding medium.

In testimony whereof, I have signed my name to this specification this 21st day of September, 1926.

RUSSELL S. OHL.

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